The present invention relates generally to building materials, and more particularly to an environmentally-friendly building material that combines the strength and durability of concrete, with the sawability, nailability, and screwability of wood.
One challenge facing the world today is how to balance the demand for new construction materials with environmental concerns caused by the extensive use of wood. To address that challenge, xe2x80x9cgreenxe2x80x9d building technologies are being developed that use renewable or recycled resources in place of traditional materials.
One aspect of these green building technologies is the avoidance of new wood or whole wood sheeting. As is known to the art, the manufacture of whole wood sheeting creates large amounts of waste as the whole tree is under-utilized. Moreover, wood is flammable, making wood construction less safe than its non-flammable alternatives.
One alternative to wood is concrete masonry products, such as concrete blocks or bricks. These products are generally fireproof, but are difficult to use in many applications because they cannot easily be sawed, and cannot easily accept nails or screws. Special water-cooled concrete saws are normally required to cut concrete, and concrete anchors are generally needed to use nails or screws in concrete.
It can be seen from the above that a need exists for a new building material that: (1) uses renewable or recycled raw materials; (2) is fireproof; (3) can be sawed with conventional saws; and (4) can accommodate conventional nails and/or screws. The present invention addresses that need.
Briefly describing one aspect of the present invention, there is provided a method for making a fast-setting, fibrous, Portland cement-based building material. The material is preferably made by:
(a) combining absorbent fibers (preferably wood chips) with water to provide substantially saturated fibers;
(b) combining the saturated fibers with an aqueous slurry of Portland cement to provide a fiber/cement slurry;
(c) combining the fiber/cement slurry with an aqueous solution of monomagnesium phosphate (xe2x80x9cMOPxe2x80x9d) and allowing the fiber/cement/MOP mixture to begin reacting; and
(d) compressing the fiber/cement/MOP mixture as it xe2x80x9csetsxe2x80x9d to provide a fibrous, Portland Cement-based building material.
One object of the present invention is to provide a superior building material that combines the advantages of cement and wood.
Another object of the present invention is to make a superior building material from cement and recycled wood.
Other objects and advantages will be apparent from the following description.
For the purpose of providing a further understanding of the principles of the invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. All alterations, modifications, and further applications of the principles of the invention, whether preferred or not, are intended to be within the scope of the invention as broadly defined.
As indicated above, the present invention combines a water-absorbent fibrous material (such as wood chips) with Portland cement to make a fiber/cement slurry, and then combines the fiber/cement slurry with a fast-setting binding agent such as monomagnesium phosphate (xe2x80x9cMOPxe2x80x9d) to make a cementitious material. The cementitious material can be used in essentially any way that other building materials, such as wood or cement blocks, are used. Building blocks and fence posts are among the most preferred commercial embodiments.
The invention finds particular advantage in its ability to use recycled or waste wood chips as the fiber material. In some less preferred embodiments, new or recycled paper may be used in addition to, or as a replacement for, the wood chips. Alternatively, other synthetic or natural water-absorbent fillers may be used to supplement or replace the wood or paper fibers, although those embodiments are less preferred in testing to date. (For the remainder of this disclosure, wood chips will generally be used as the water-absorbent fiber material. It is to be understood though, that other fibers could be used as noted above.)
The wood chips or other water-absorbent fibrous material is preferably sized between xe2x80x9cmulchxe2x80x9d-sized chips and wood xe2x80x9cshavings.xe2x80x9d Most commonly, a majority of the wood chip material is provided by chips that are between about 0.50xe2x80x3 and 1.50xe2x80x3 in length (12 to 38 mm), with chips between 0.50xe2x80x3 and 1.0xe2x80x3 long being more preferred. Similarly, a substantial portion of the wood chip material is provided by chips that are between about 0.125xe2x80x3 to 0.50xe2x80x3 thick (3 to 12 mm), with chips between 0.125xe2x80x3 and 0.25xe2x80x3 thick being more preferred. Lastly, a substantial portion of the wood chip material is provided by chips that are between about 0.125xe2x80x3 to 1.0xe2x80x3 wide (3 to 25 mm), with chips between 0.25xe2x80x3 and 0.50xe2x80x3 wide being more preferred. Pieces within or near those size ranges are generally large enough to provide structural integrity to the finished product, yet small enough to be held firmly in the cement/MOP matrix. The appropriate size will depend somewhat on the fiber material being used, the consistency of the cement and the MOP, and the end use for the finished product.
Further as to wood chip size, while it is appreciated that the particles may be of various sizes, a substantial volume of the fibers should be large enough to grip and/or hold a nail or screw when penetrated. Preferably, the pieces are large enough that at least 25% of the volume of the chips can be compressed by 50% when penetrated by a nail or screw, thus allowing for tight penetration.
Although in some embodiments dry fibers are used, in the most preferred embodiments the fibers are soaked in water before being added to the cement. It is believed that soaking fills the spaces in the fibers with water, and allows the cement/MOP matrix to more easily enter and fill those spaces. When pre-soaking is used, it should be for a time sufficient to substantially saturate the wood chips (or other fibers), with 50-100% saturation being preferred, 60-95% saturation being more preferred, and 70-90% saturation being most preferred.
After soaking, the fibrous material is preferably drained to remove any residual waterxe2x80x94particularly water that remains on the surface of the material. It is not necessary that the surface of the saturated material be dry, but it is preferred that the amount of water surrounding (as opposed to within) the fibrous material be minimized. Generally, it is preferred that the wood chips or other fibers be wet, but not dripping wet. In certain embodiments though (and particularly when less water is used in the Portland cement slurry that is combined with the fibers) dripping wet fibers can be used.
While the wood chips or other fibers are soaking or draining the Portland cement slurry can be prepared. Generally, the Portland cement slurry is prepared by combining dry Portland cement with water at a ratio of between about 1:1 to 4:1 (cement:water). In the most preferred embodiment a ratio of about 2:1 (cement:water) is used. The cement slurry is mixed until smooth, as is known to the art.
When the xe2x80x9csaturatedxe2x80x9d fibers and the cement slurry are both ready, the two components are mixed together to make a wet cement/fiber mixture. Preferably, the ratio of wet fiber to wet cement in the cement/fiber mixture is between about 1:2 and 1:4 (weight-to-weight), with 1:3 being most preferred. The components are mixed until the wood chips or other fibers are well coated.
In an alternative embodiment the cement slurry is made by adding dry cement and water to the saturated wood chips and mixing thoroughly to make the cement/wood chip slurry. This embodiment eliminates the need to add the wood chips to the cement slurry after the slurry is mixed.
As to the binding agent, monomagnesium phosphate (xe2x80x9cMOPxe2x80x9d) is most preferred in testing to date. The MOP is mixed with water, with a ratio of about 2:1 (MOP:water) being preferred for most applications. In alternative applications MOP:water ratios may vary from 4:1 to about 1:1.
When the MOP is initially combined with the water, the MOP particles do not immediately go into solution. Accordingly, the MOP and water are preferably mixed for several minutes (preferably between about 20 and 40 minutes) until the MOP and water combine to form a xe2x80x9ccreamyxe2x80x9d solution. It is this well-mixed MOP/water preparation that is combined with the cement/fiber slurry prepared above.
As previously indicated, the material of the present invention is prepared by mixing the MOP/water preparation with the cement/fiber slurry. The mixing serves to ensure that the components are fairly evenly distributed, and proceeds until the MOP begins to xe2x80x9creactxe2x80x9d with the fiber/cement slurry. The reaction is exothermic, so the mixing may be stopped when the mixture begins to get warm and xe2x80x9cset.xe2x80x9d
The last step in the preparation of the inventive material is the compression step. In this step the material is xe2x80x9cpressedxe2x80x9d with a force of at least about 50 psi, most preferably in a mold to shape the product. In the most preferred embodiments the material is pressed using a force of between about 200 and 2000 psi.
It is to be appreciated that the cementitious material is substantially fireproof, much as conventional cement is. It is also to be appreciated that the cementitious material has properties that are not possessed by conventional cement. For example, the cementitious material is sawable (can be sawed with a conventional saw), and nailable (can be nailed with conventional nails), much as wood is. Moreover, screws can be used without the anchors required by conventional concrete.
Reference will now be made to specific examples using the processes described above. It is to be understood that the examples are provided to more completely describe preferred embodiments, and that no limitation to the scope of the invention is intended thereby.